ANSI Common Lisp 13 Characters 13.2 Dictionary of Characters
The type base-char is defined as the upgraded array element type
An implementation can support additional subtypes of type character
(besides the ones listed in this standard)
that might or might not be supertypes of type base-char.
In addition, an implementation can define base-char
to be the same type as character.
Base characters are distinguished in the following respects:
Whether a character is a base character depends on the way
that an implementation represents strings,
and not any other properties of the implementation or the host operating system.
For example, one implementation might encode all strings
as characters having 16-bit encodings, and another might have
two kinds of strings: those with characters having 8-bit
encodings and those with characters having 16-bit encodings. In the
first implementation, the type base-char is equivalent to
the type character: there is only one kind of string.
In the second implementation, the base characters might be
those characters that could be stored in a string of characters
having 8-bit encodings. In such an implementation,
the type base-char is a proper subtype of the type character.
The type standard-char is a
subtype of type base-char.
- Allegro CL Implementation Details: